Q. I have been practicing my TIG welding on 1/8-inch aluminum after viewing your TIG DVD. Sometimes, after welding, the aluminum is dull and grainy instead of bright and smooth. I'm having particular trouble at the end of the weld. I have tried putting a spot weld on the panel to stop at, but I still overheat the metal and melt the heck out of it.
Via the Internet
A. All of your symptoms suggest overheating. As you weld across a workpiece, it takes a lot of heat to start, since normally the metal is at room temperature. As you progress a few inches from the start, the metal around the weld has gained some heat, so less "foot pedal" is needed to maintain the puddle at the optimum size. As you approach the end of the workpiece, there is a smaller "escape path" for all the heat that you've been pouring into the metal, so you need to "let up on the foot pedal" even more as you are approaching the end.
With lots of practice this becomes automatic-but as you are learning, pay special attention to the width of the weld puddle-that's a good indication of how much heat you're putting into the metal.